Crust Fungus
A Stereum crust fungus, probably Stereum gausapatum, growing on the trunk of a dead birch tree (Betula sp). This fungus is recognizable by its mainly ochre and grey colour, white margins, and by the fact that it bleeds red liquid when scratched:
Photos taken in the Wilderness, Whiteknights Park, Reading, UK, on 2012-11-22.